Component property derived from a custom class - delphi

Question

I create my own class and I want to use it in my new component but I am getting an error...
The code is the following:
type
TMyClass = class
Name: string;
Number: double;
end;
TMyComponent = class(TCustomPanel)
private
FMyClass: TMyClass;
public
procedure SetMyClass(aName: string; aNumber: double);
published
property MyClass: TMyClass write SetMyClass;
end;
procedure SetMyClass(aName: string; aNumber: double);
begin
FMyClass.Name:= aName;
FMyClass.Number:= aNumber;
end;
it appears that the property has incompatible types, I don't know why.
Does anybody has a clue about that and how can I solve this problem.
Having a FName and FNumber as fields in TMyComponent is not an option, my code is more complex and this is a simple example to explain my goal.
thanks

Answer 1

The things that I can see wrong with your code at present are:
The property setter must receive a single parameter of the same type as the property, namely TMyClass.
The property setter must be a member of the class, but you've implemented it as a standalone procedure.
A published property needs to have a getter.
So the code would become:
type
TMyClass = class
Name: string;
Number: double;
end;
TMyComponent = class(TCustomPanel)
private
FMyClass: TMyClass;
procedure SetMyClass(Value: TMyClass);
published
property MyClass: TMyClass read FMyClass write SetMyClass;
end;
procedure TMyComponent.SetMyClass(Value: TMyClass);
begin
FMyClass.Name:= Value.Name;
FMyClass.Number:= Value.Number;
end;
This code does not instantiate FMyClass. I'm guessing that the code that does instantiate FMyClass is part of the larger component code that has been excised for the sake of this question. But obviously you do need to instantiate FMyClass.
An alternative to instantiating FMyClass is to turn TMyClass into a record. Whether or not that would suit your needs I cannot tell.
It looks like you are having some problems instantiating this object. Do it like this:
type
TMyClass = class
Name: string;
Number: double;
end;
TMyComponent = class(TCustomPanel)
private
FMyClass: TMyClass;
procedure SetMyClass(Value: TMyClass);
public
constructor Create(AOwner: TComponent); override;
destructor Destroy; override;
published
property MyClass: TMyClass read FMyClass write SetMyClass;
end;
constructor TMyComponent.Create(AOwner: TComponent);
begin
inherited;
FMyClass:= TMyClass.Create;
end;
destructor TMyComponent.Destroy;
begin
FMyClass.Free;
inherited;
end;
procedure TMyComponent.SetMyClass(Value: TMyClass);
begin
FMyClass.Name:= Value.Name;
FMyClass.Number:= Value.Number;
end;
One final comment. Using MyClass for an object is a bad name. Use class for the type, and object for the instance. So, your property should be MyObject and the member field should be FMyObject etc.

Answer 2

Try this:
type
TMyClass = class
Name: string;
Number: double;
end;
TMyComponent = class(TCustomPanel)
private
FMyClass: TMyClass;
public
procedure SetMyClass(Value: TMyClass);
published
property MyClass: TMyClass write SetMyClass;
end;
procedure TMyComponent.SetMyClass(Value);
begin
FMyClass := Value;
end;

Answer 3

unit MyComponentTest2;
interface
uses SysUtils, Classes, Controls, Forms, ExtCtrls, Messages, Dialogs;
type
TMyClass = class
Name: string;
Number: double;
end;
TMyComponentTest2 = class(TCustomPanel)
private
FMyClass: TMyClass;
public
constructor Create(AOwner: TComponent); override;
destructor Destroy; override;
procedure SetMyClass(Value: TMyClass);
published
property MyClass: TMyClass read FMyClass write SetMyClass;
end;
procedure Register;
implementation
constructor TMyComponentTest2.Create(AOwner: TComponent);
begin
Inherited Create(AOwner);
FMyClass:= TMyClass.Create;
end;
destructor TMyComponentTest2.Destroy;
begin
Inherited;
FMyClass.Free;
end;
procedure TMyComponentTest2.SetMyClass(Value: TMyClass);
begin
FMyClass.Name:= Value.Name;
FMyClass.Number:= Value.Number;
end;
procedure Register;
begin
RegisterComponents('MyComponents', [TMyComponentTest2]);
end;
end.